Not Applicable
Not Applicable
It is well understood that stents which are not properly secured or retained to the catheter may slip and either be lost or be deployed in the wrong location or partially deployed. Traditionally, in order to provide proper securement of the stent on the catheter the stent is crimped to a predetermined area of the catheter.
In the past, crimping has been done by hand or by a crimping apparatus, often resulting in the application of undesired uneven forces to the stent. Such a stent must either be discarded or re-crimped. Stents which have been crimped multiple times can suffer from fatigue and may be scored or otherwise marked which can cause thrombosis. A poorly crimped stent can also damage the underlying balloon.
Stents and stent delivery assemblies are utilized in a number of medical procedures and situations, and as such their structure and function are well known. A stent is a generally cylindrical prosthesis introduced via a catheter into a lumen of a body vessel in a configuration having a generally reduced diameter and then expanded to the diameter of the vessel. In its expanded configuration, the stent supports and reinforces the vessel walls while maintaining the vessel in an open, unobstructed condition.
The present invention avoids these problems by providing ribbed stent retaining sleeves which are capable of securing a stent to the catheter without the need to crimp the stent into place. The ribbed sleeves may be utilized with nearly any type of stent. Both self-expanding and inflation expandable stents are well known and widely available in a variety of designs and configurations. Self-expanding stents must be maintained under a contained sheath or sleeve(s) in order to maintain their reduced diameter configuration during delivery of the stent to its deployment site. Inflation expandable stents are crimped to their reduced diameter about the delivery catheter, then maneuvered to the deployment site and expanded to the vessel diameter by fluid inflation of a balloon positioned between the stent and the delivery catheter. The present invention is particularly concerned with delivery and deployment of inflation expandable stents, although it is generally applicable to self-expanding stents when used with balloon catheters.
In advancing an inflation expandable stent through a body vessel to the deployment site, there are a number of important considerations. The stent must be able to securely maintain its axial position on the delivery catheter without translocating proximally or distally and especially without becoming separated from the catheter. The stent, particularly its distal and proximal ends, must be protected to prevent distortion of the stent and to prevent abrasion and/or reduce trauma of the vessel walls.
Inflation expandable stent delivery and deployment assemblies are known which utilize restraining means that overlie the stent during delivery. U.S. Pat. No. 4,950,227 to Savin et al., relates to an inflation expandable stent delivery system in which a sleeve overlaps the distal or proximal margin (or both) of the stent during delivery. During inflation of the stent at the deployment site, the stent margins are freed of the protective sleeve(s). U.S. Pat. No. 5,403,341 to Solar, relates to a stent delivery and deployment assembly which uses retaining sheaths positioned about opposite ends of the compressed stent. The retaining sheaths of Solar are adapted to tear under pressure as the stent is radially expanded, thus releasing the stent from engagement with the sheaths. U.S. Pat. No. 5,108,416 to Ryan et al., describes a stent introducer system which uses one or two flexible end caps and an annular socket surrounding the balloon to position the stent during introduction to the deployment site.
Another invention which may be relevant to the present invention is disclosed in a concurrently filed and commonly assigned U.S. patent application entitled: U.S. Application entitled FULLY SHEATHED EXPANDABLE STENT DELIVERY SYSTEM, designated by U.S. application Ser. No. 09/552807.
All of the references contained herein, including the co-pending Application listed above, are respectively incorporated in their entirety herein by reference.
This invention provides an improvement over the prior art, by providing a stent delivery system which includes one or more stent retaining sleeves having a ribbed configuration. The ribbed configuration provides the one or more sleeves with a reduced columnar strength and improved radial strength characteristics. The ribbed sleeves of the present invention are capable of retaining and immobilizing a non-crimped stent on the catheter surface by completely covering all or only a portion of the stent, the sleeves are readily retracted from off of the stent to provide for safe and effective stent release.
The sleeve or sleeves have a ribbed configuration. The ribbed configuration provides a plurality of alternating raised and lowered pleats, with the lowered pleats contacting the stent. The sleeve or sleeves may be composed of an elastic polymer, a non-elastic polymer or a combination thereof.
The reduced columnar strength of the sleeves is at least in part a consequence of having only the downward pleats of the sleeves, rather than the entire sleeve, frictionally engage the stent surface. The reduced columnar strength provided by this arrangement allows the sleeves to be retracted from the stent without the need to apply lubrication to the stent/sleeve surfaces.
The ribbed configuration of the sleeves further provides a spring or recoil action to the sleeves which is triggered when the stent is expanded. The recoil action of each sleeve is directed in longitudinally opposing directions and assists in actively retracting the sleeves off of the stent in the appropriate direction. The combination of the recoil action and the reduced columnar strength of the sleeves, allows the sleeves to be pulled completely off of the stent with improved effectiveness.
As may be understood from viewing the various figures included herein, the unique physical characteristics of the present sleeves, most notably the recoil action, provides the present invention with the capacity to include sleeves which may be fitted over increased areas of the stent as opposed to merely the stent edges or ends as provided for in many prior stent delivery systems. By providing sleeves which may cover the entire stent the present invention helps to ensure that the stent is completely immobilized on the stent surface. In addition, the potentially increased coverage provided by the sleeves reduces the potential for accidental or premature stent delivery and may help to protect the stent from damage prior to and during stent delivery.
The ribbed configuration of the sleeves also provides the sleeves with radial strength characteristics sufficient to provide an interference fit between each of the sleeves and the stent. The interference fit retains the sleeves in a desired position and in a reduced configuration until the recoil action is triggered by the expansion of the stent. The radial strength characteristics of the ribbed sleeves are such that even during the retraction of the sleeves the interference fit is maintained, thus providing a uniform and consistent retraction of the sleeves while also ensuring that the retracted sleeves do not interfere with the safe removal of the catheter from the vessel subsequent to stent delivery.